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G.R. Meurer, D. Thilker, L. Bianchi (The Johns Hopkins University), A. Ferguson (Max-Planck-Institut fuer Astrophysik), B. Madore, A. Gil de Paz (Carnegie Observatory), S. Hameed (Smith College & FCAD), GALEX Science Team
Much of what we know about star formation in galaxies comes from the observation of H-alpha, the most easily accessible high mass star formation tracer, which indicates the presence of ionizing O stars (M > ~20 M\sun). The launch of GALEX provides ready access to high quality observations of another important, more direct high mass star formation tracer - the far ultraviolet (FUV). The FUV is sensitive to photospheric emission from both O and B stars (M > ~8 M\sun) and thus to the full mass range of stars with the largest impact on the ISM through ionization, dissociation of H2, stellar winds, and supernovae explosions. Comparison of GALEX FUV and terrestial H-alpha observations of nearby disk galaxies show that typically (but not always) the UV emission extends considerably further than the H-alpha. While the H-alpha distributions often show a marked edge, as originally noted by Kennicutt (1989), the UV distributions do not (Thilker et al., ApJL, in press; Bianchi et al., ApJL in press). This result has enormous implications for galactic evolution, particularly our understanding of the star formation law, the initial mass function, modes of star formation, the stability of extended HI disk galaxies, and star formation surveys. We examine these implications and explore possible explanations for the different distributions of these important star formation tracers.
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Bulletin of the American Astronomical Society, 36 5
© 2004. The American Astronomical Society.